Threshold current modifying device and method

ABSTRACT

A threshold current modifying device is provided for an optical pickup head. The optical pickup head initially generates an output power when an operating current is larger than a threshold current of the optical pickup head, and the threshold current is related to a temperature of the optical pickup head in a function relationship. The threshold current modifying device includes a threshold current calculating module and a power control module. The threshold current calculating module receives a temperature signal from the optical pickup head at a first temperature to output a threshold current signal according to the temperature signal and the function relationship. The power control module receives the threshold current signal to adjust the operating current.

BACKGROUND OF THE INVENTION

1. Field of Invention

The invention relates to a threshold current modifying device and athreshold current modifying method, and, in particular, to a thresholdcurrent modifying device and a threshold current modifying method, whichare applicable to an optical disk drive.

2. Related Art

An electric device is sensitive to temperature such that the performanceand accurate of the electric device may be affected by surroundingtemperature the electric device locates. In order to control theelectric device at different temperatures, a proper control module mustbe designed to modify the affection resulted from the thermal factor.

In order to control the output power of the electric device at differenttemperatures, a proper control module is designed in the electricdevice. Herein, a power feedback signal, which is generated when theelectric device generates the output power, is applied to control theoperating current for driving the electric device to generate the outputpower at different powers.

Referring to FIG. 1A, when the temperature of the electric device is ata temperature T₁, a relationship between the output power and theoperating current of the electric device is represented as a line L₁. Inother words, when the operating temperature of the electric device is atthe temperature T₁ and the operating current is at a current I₁, theelectric device generates the output power at a power P₁. If theoperating current is at a current I₂, the electric device generates theoutput power at a power P₂. If the temperature of the electric deviceraises to a temperature T₂, the control module increases the operatingcurrent according to the power feedback signal until the electric devicegenerates the output power at the power P₁. At the same time, theoperating current is equal to current I₁′. In addition, the priortechnique regards that a line L₂ represents a relationship between theoutput power and the operating current of the electric device at thetemperature T₂. In order to control the electric device to generate theoutput power at a power P₂, the control module calculates the requiredcurrent I₂′ to drive the electric device to generate the output power atthe power P₂ according to the operating current variance (I₁′−I₁)resulting from the temperature variance for the power P₁, and a scalerelationship between the power P₁′ and the power P₂ in lines L₁ and L₂.The calculation is shown as the following formula (1). $\begin{matrix}{I_{2}^{\prime} = {{\frac{P_{2}}{P_{1}}\left( {I_{1}^{\prime} - I_{1}} \right)} + I_{2}}} & (1)\end{matrix}$

In fact, when the temperature of the electric device is at a temperatureT₂, the output power and the operating current of the electric deviceare actually related in a line L₃ rather than the line L₂. Therefore,the calculated operating current, which is equal to a current I₂, drivesthe electric device to generate the output power at the power P₃. Thus,the electric device does not correctly generate the output power at thepower P₂ and the output power is not precisely controlled at thetemperature T₂.

Because the prior technique disregards the threshold currents(intersections of the line L₁, line L₃ and the current axis), an errorbetween the power P₂ and power P₃ occurs. If the threshold current isineffectual, the error caused by the prior technique is not obvious. Inother words, when the temperature of the electric device is at thetemperature T₂, the actual line L₃ is close to the line L₂ referred bythe prior technique. However, if the threshold current is effectual orthe output power is to be controlled more precisely, the error caused bythe operating current calculated according to the prior technique isinevitable.

Taking an optical disk drive for an example, an optical pickup head ofthe optical disk drive is easily affected by thermal factors and behavessuch as the electric device described above. Referring to FIG. 1B andFIG. 1C, in the power control structure of the optical pickup head inthe optical disk drive, an optical disk drive 1 includes an opticalpickup head 10 and a power control module 15. The optical pickup head 10includes a light-emitting module 11, a temperature measuring module 12,a light-sensing module 13, and a digital-to-analog converting module 14.The temperature measuring module 12 measures the temperature of thelight-emitting module 11 to output a temperature signal 121. Thelight-sensing module 13 senses the output power of the light-emittingmodule 11 to generate a power feedback signal 131. The power controlmodule 15 receives the temperature signal 121 and the power feedbacksignal 131 to generate a current control signal 151 in the above method.The digital-to-analog converting module 14 receives the current controlsignal 151 to generate an operating current 141. The operating current141 drives the light-emitting module 11 to generate output powers P₁ andP₂. The output powers P₁ and P₂ are respectively a writing power P_(w)and a reading power P_(r) for accessing an optical disk. However, if thetemperature of the light-emitting module raises, only the reading powerP₁ is precisely controlled but the writing power P_(w) due to thedisregarded threshold currents. Therefore, the optical pickup head 10does not correctly access the optical disk, and, even more, the lifetimeof the optical pickup head 10 and the endurance of the optical diskdrive 1 are reduced.

It is therefore a subject of the invention to provide a thresholdcurrent modifying device and a threshold current modifying method, whichcalculate the threshold current of the electric device of differenttemperatures. Thus, the output power of the electric device can beprecisely controlled.

SUMMARY OF THE INVENTION

In view of the foregoing, the invention is to provide a thresholdcurrent modifying device and a threshold current modifying method, whichcan calculate the threshold current of an electric device according tothe different temperatures thereof.

To achieve the above, a threshold current modifying device is providedfor an optical pickup head. The optical pickup head initially generatesan output power when an operating current is larger than a thresholdcurrent of the optical pickup head, and the threshold current is relatedto a temperature of the optical pickup head in a function relationship.The threshold current modifying device includes a threshold currentcalculating module and a power control module. The threshold currentcalculating module receives a temperature signal from the optical pickuphead at a first temperature and then outputs a threshold current signalaccording to the temperature signal and the function relationship. Thepower control module receives the threshold current signal to adjust theoperating current.

To achieve the above, a threshold current modifying method is providedfor an optical pickup head. The optical pickup head initially generatesan output power when an operating current is larger than a thresholdcurrent of the optical pickup head, and the threshold current is relatedto a temperature of the optical pickup head in a function relationship.The threshold current modifying method includes the following steps of:measuring the first temperature of the optical pickup head; outputting athreshold current signal according to the first temperature and thefunction relationship; and adjusting the operating current according tothe threshold current signal.

As mentioned above, since the threshold current modifying device andmethod according to the invention control the operating current based onthe temperature of the electric device and the function relationship.Thus, the threshold current for different output powers and temperaturesin the electric device is calculated, such that the output power of theelectric device is precisely controlled.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will become more fully understood from the detaileddescription given herein below illustration only, and thus is notlimitative of the present invention, and wherein:

FIG. 1A is a curve relation diagram showing the output power and theoperating current of the conventional electric device;

FIG. 1B is a block diagram showing the power control structure of theoptical pickup head in the optical disk drive;

FIG. 1C is a schematic view showing the writing power and the readingpower of the conventional optical pickup head;

FIG. 2 is a block diagram showing a threshold current modifying deviceaccording to a preferred embodiment of the invention;

FIG. 3 is another block diagram showing the threshold current modifyingdevice according to the preferred embodiment of the invention;

FIG. 4A is a curve relation diagram showing the temperature and thethreshold current of the optical read/write module in the thresholdcurrent modifying device according to the preferred embodiment of theinvention;

FIG. 4B is a relation table showing the temperature and the thresholdcurrent of the optical read/write module in the threshold currentmodifying device according to the preferred embodiment of the invention;

FIG. 5 is a curve relation diagram showing the output power and theoperating current of the optical read/write module in the thresholdcurrent modifying device according to the preferred embodiment of theinvention;

FIG. 6 is a schematic view showing the reading power and the writingpower of the optical pickup head in the threshold current modifyingdevice according to the preferred embodiment of the invention; and

FIG. 7 is a flow chart showing a threshold current modifying methodaccording to a preferred embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be apparent from the following detaileddescription, which proceeds with reference to the accompanying drawings,wherein the same references relate to the same elements.

Referring to FIG. 2, a threshold current modifying device 2 according toa preferred embodiment of the invention is provided for an opticalpickup head 4. The optical pickup head 4 initially generates an outputpower when an operating current is larger than a threshold current ofthe optical pickup head 4. The threshold current is related to atemperature of the optical pickup head 4 in a function relationship.

In this embodiment, the threshold current modifying device 2 includes athreshold current calculating module 21 and a power control module 22.The threshold current calculating module 21 receives a temperaturesignal 31 of the optical pickup head 4 at a first temperature, then thethreshold current calculating module 21 outputs a threshold currentsignal 32 in accordance with the temperature signal 31 and the functionrelationship. The power control module 22 receives the threshold currentsignal 32 to generate a current control signal 33 for adjusting theoperating current of the optical pickup head 4.

Referring to FIG. 3, in this embodiment, the optical pickup head 4 andthe threshold current modify device 2 are applied to an optical diskdrive 5. The optical pickup head 4 includes a light-emitting module 41,a light-sensing module 42, a temperature measuring module 43, and adigital-to-analog converting module 44.

In the optical pickup head 4, an operating current 34 drives thelight-emitting module 41 to generate an output power. The light-sensingmodule 42 measures the output power of the light-emitting module 41 togenerate a power feedback signal 35 applied for the power control module22 to monitor the output power of the light-emitting module 41. Besides,the temperature measuring module 43 measures the temperature of thelight-emitting module 41 to output a temperature signal 31, and thedigital-to-analog converting module 44 receives the current controlsignal 33 from the power control module 22 to generate the operatingcurrent 34.

Please refer to FIG. 3 again, in the threshold current modifying device2, the threshold current calculating module 21 includes atemperature-to-threshold current table 211 and a threshold currentlooking-up unit 212. In addition, the threshold current modifying device2 includes an analog-to-digital converting module 23. In details, thetemperature-to-threshold current table 211 is a corresponding table forthe function relationship between the temperature and the thresholdcurrent of the optical pickup head 4. The temperature-to-thresholdcurrent table 211 records the threshold currents corresponding tovarious temperatures of the light-emitting module 41. The thresholdcurrent looking-up unit 212 receives the temperature signal 31 and looksa threshold current up in the temperature-to-threshold current table 211to output the threshold current signal 32 according to the firsttemperature. In addition, the analog-to-digital converting module 23converts the temperature signal 31 from analog to digital, then thetemperature signal 31 is processed by the threshold current looking-upunit 212.

In this embodiment, because the function relationship between thetemperature of the light-emitting module 41 and the threshold current isexponential relationship (as shown in FIG. 4A), this exponentialrelationship could be quantified and stored in thetemperature-to-threshold current table 211 of the threshold currentmodifying device 2 (as shown in FIG. 4B).

In addition, referring to FIG. 3 and FIG. 5. When the temperature of thelight-emitting module 41 is at first temperature T₁, the light-emittingmodule 41 and the operating current 34 is related in a line L₁. At thistime, the power control module 22 controls the digital-to-analogconverting module 44 according to the power feedback signal 35.Therefore, the operating current 34 generated by the digital-to-analogconverting module 44 is equal to current I₁, and drives thelight-emitting module 41 to generate the output power P₁.

Besides, if the power control module 22 controls the light-emittingmodule 41 to generate the output power P₂, the threshold currentlooking-up unit 212 receives the temperature signal 31 and looks a firstthreshold current I_(t1) of the first temperature T₁ up in thetemperature-to-threshold current table 211 to output the thresholdcurrent signal 32 according to the first temperature. Then, the powercontrol module 22 receives the threshold current signal 32 andcalculates the current I₂ for generating the output power P₂ inaccordance with the formula (2). After that, the power control module 22outputs the calculation as a current control signal 231. $\begin{matrix}{I_{2} = {I_{t\quad 1} + {\frac{P_{2}}{P_{1}}\left( {I_{1} - I_{t\quad 1}} \right)}}} & (2)\end{matrix}$

The digital-to-analog converting module 44 receives the current control231 to adjust the operating current 34 to be I₂ such that the operatingcurrent 34 drives the light-emitting module 41 to generate the outputpower P₂ correctly.

Please refer to FIG. 3 and FIG. 5 again. When the temperature of thelight-emitting module 41 is at temperature T₂, the output power of thelight-emitting module 41 and the operating current 34 are related in aline L₂ in FIG. 5. After the temperature of the light-emitting module 41arises to temperature T₂, the light-sensing module 42 measures theoutput power of the light-emitting module 41 to generate the powerfeedback signal 35. The power control module 22 and thedigital-to-analog converting module 44 raise the operating current 34 tobe I_(I)′ according to the power feedback signal 35, such that theoperating current 34 drives the light-emitting module 41 to generate theoutput power P₁ correctly.

At this time, when the light-emitting module 41 is going to generate theoutput power P₂, the temperature measuring module 43 measures the secondtemperature T₂ of the light-emitting module 41 to output the temperaturesignal 31. The threshold current looking-up unit 212 receives thetemperature signal 31 and looks a second threshold currents I_(t2) ofthe second temperature T₂ up in the temperature-to-threshold currenttable according to the second temperature T₂. Then, the thresholdcurrent looking-up unit 212 computes the difference between the firstthreshold current I_(t1) and the second threshold current I_(t2) tooutput the threshold current signal 32 (I_(t1)−I_(t2)).

Following, the power control module 22 receives the threshold currentsignal 32 (I_(t2)−I_(t1)), and calculates the needed current I₂′ fordriving the light-emitting module 41 to generate output power P₂ at thetemperature T₂ according to the threshold current signal 32, theproportional relationship between the output power P₁ and the outputpower P₂, and the current difference (I₁′−I₁) resulting from thetemperature difference while generating the output power P₁. Thecalculation is shown in the formula (3) and is output as the currentcontrol signal 231. $\begin{matrix}{I_{2}^{\prime} = {\left( {I_{t\quad 2} - I_{t\quad 1}} \right) + {\frac{P_{2}}{P_{1}}\left( {I_{1}^{\prime} - I_{1}} \right)} + I_{2}}} & (3)\end{matrix}$

The digital-to-analog converting module 44 receives the current controlsignal 231 to adjust the operating current 34, such that the operatingcurrent 34 drives the light-emitting module 41 to generate the outputpower P₂ correctly.

Referring to FIG. 6, the output power P₁ and the output power P₂ couldbe a reading power and a writing power of the optical pickup head 4respectively. By the process mentioned above, the reading power P₁ andthe writing power P₂ of the optical pickup head are not affected bytemperature and are controlled precisely. Hence, the optical pickup head4 accesses the optical disk accurately, and then the optical disk drive5 operates regularly.

Please refer to FIG. 3 again. The threshold current modifying device 2could be implemented with an integrated circuit. The integrated circuitincludes the circuit implementing the threshold current calculatingmodule 21 and the power control module 22. The integrated circuit couldbe a chip, a digital signal processor, a microcontroller, or the likes.

Referring to FIG. 7, a threshold current modifying method is providedfor a optical pickup head. The optical pickup head initially generatesan output power when an operating current is larger than a thresholdcurrent of the optical pickup head, and the threshold current is relatedto a temperature of the optical pickup head in a function relationship.The threshold current modifying method includes the steps S01-S03.

The step S01 measures the first temperature of the optical pickup head.

The step S02 outputs a threshold current signal according to the firsttemperature and the function relationship. In this embodiment, the stepS02 looks a first threshold current of the first temperature up in atemperature-to-threshold current table in accordance with the firsttemperature to output the threshold current signal. Thetemperature-to-threshold current table is a corresponding table of thefunction relationship between the temperature and the threshold currentof the optical pickup head, and records the first threshold currentcorresponding to the first temperature.

The step S03 adjusts the operating current according to the thresholdcurrent signal.

In the embodiment, the threshold current modifying method may furtherinclude steps S04 to S05.

The step S04 measures a second temperature of the optical pickup head.

The step S05 outputs a threshold current signal according to the firsttemperature, the second temperature and the function relationship. Inthis embodiment, the step S02 looks a second threshold current of thesecond temperature up in a temperature-to-threshold current table inaccordance with the second temperature, and then computes a differencebetween the first threshold current and the second threshold current tooutput the threshold current signal.

The threshold current modifying method according to the embodiment canbe applied to the threshold current modifying device mentioned in theabove embodiment as shown in FIG. 2 to FIG. 6. Thus, the thresholdcurrent modifying method of this embodiment can be realized withreferring to the previous embodiment, and the detailed descriptions areomitted here.

In summary, since the threshold current modifying device and methodaccording to the invention control the operating current based on thetemperature of the electric device and the function relationship. Thus,the threshold current for different output powers and temperatures inthe electric device is calculated, such that the output power of theelectric device is precisely controlled.

Although the invention has been described with reference to specificembodiments, this description is not meant to be construed in a limitingsense. Various modifications of the disclosed embodiments, as well asalternative embodiments, will be apparent to persons skilled in the art.It is, therefore, contemplated that the appended claims will cover allmodifications that fall within the true scope of the invention.

1. A threshold current modifying device for an optical pickup head,wherein the optical pickup head generates an output power when anoperating current is larger than a current threshold of the opticalpickup head, and the current threshold is related to a temperature ofthe optical pickup head in a function relationship, the thresholdcurrent modifying device comprising: a threshold current calculatingmodule for receiving a temperature signal from the optical pickup headat a first temperature to output a threshold current signal according tothe temperature signal and the function relationship; and a powercontrol module for receiving the threshold current signal to adjust theoperating current.
 2. The threshold current modifying device as recitedin claim 1, wherein the threshold current calculating module comprises:a temperature-to-threshold current table for recording the firstthreshold current corresponding to the first temperature, wherein thetemperature-to-threshold current table is a corresponding table of thefunction relationship between the temperature and the threshold currentof the optical pickup head; and a threshold current looking-up unit forreceiving the temperature signal and looking the first threshold currentup in the temperature-to-threshold current table to output the thresholdcurrent signal according to the first temperature.
 3. The thresholdcurrent modifying device as recited in claim 1, wherein the thresholdcurrent calculating module receives the temperature signal from theoptical pickup head at the second temperature to output the thresholdcurrent signal according to the first temperature, the secondtemperature and the function relationship.
 4. The threshold currentmodifying device as recited in claim 3, wherein the threshold currentcalculating module comprises: a temperature-to-threshold current tablefor recording the first threshold current and the second thresholdcurrent corresponding to the first temperature and the secondtemperature respectively, wherein the temperature-to-threshold currenttable is a corresponding table of the function relationship between thetemperature and the threshold current of the optical pickup head; and athreshold current looking-up unit for receiving the temperature signal,looking the first and the second threshold currents up in thetemperature-to-threshold current table according to the firsttemperature and the second temperature respectively, and computing thedifference between the first threshold current and the second thresholdcurrent to output the threshold current signal.
 5. The threshold currentmodifying device as recited in claim 1, wherein the functionrelationship is an exponential relationship.
 6. The threshold currentmodifying device as recited in claim 1, wherein the optical pickup headcomprises: a digital-to-analog converting module controlled by the powercontrol module to generate the operating current; a light-emittingmodule driven by the operating current to generate the output power; anda temperature measuring module measuring the first temperature of thelight-emitting module to generate the temperature signal.
 7. Thethreshold current modifying device as recited in claim 1, wherein thethreshold current modifying device and the optical pickup head areinstalled in an optical disk drive.
 8. The threshold current modifyingdevice as recited in claim 1, wherein the threshold current calculatingmodule and the power control module are implemented with an integratedcircuit.
 9. A threshold current modifying method for an optical pickuphead, wherein the optical pickup head initially generates an outputpower when an operating current is larger than a threshold current ofthe optical pickup head, and the threshold current is related to atemperature of the optical pickup head in a function relationship, thethreshold current modifying method comprising: measuring the firsttemperature of the optical pickup head; outputting a threshold currentsignal according to the first temperature and the function relationship;and adjusting the operating current according to the threshold currentsignal.
 10. The threshold current modifying method as recited in claim9, wherein the outputting step looks a first threshold current up in atemperature-to-threshold current table in accordance with the firsttemperature to output the threshold current signal, and thetemperature-to-threshold current table is a corresponding table of thefunction relationship between the temperature and the threshold currentof the optical pickup head, and records the first threshold currentcorresponding to the first temperature.
 11. The threshold currentmodifying method as recited in claim 9, further comprising: measuring asecond temperature of the optical pickup head; and outputting thethreshold current signal in accordance with the first temperature, thesecond temperature and the function relationship.
 12. The thresholdcurrent modifying method as recited in claim 9, further comprising:measuring a second temperature of the optical pickup head; looking afirst threshold current up in a temperature-to-threshold current tablein accordance with the first temperature; looking a second thresholdcurrent up in the temperature-to-threshold current table in accordancewith the second temperature, wherein the temperature-to-thresholdcurrent table is a corresponding table of the function relationshipbetween the temperature and the threshold current of the optical pickuphead, and records the first threshold current and the second thresholdcurrent corresponding to the first temperature and the secondtemperature respectively; and computing the difference between the firstthreshold current and the second threshold current to output thethreshold current signal.
 13. The threshold current modifying method asrecited in claim 9, wherein the function relationship is an exponentialrelationship.
 14. The threshold current modifying method as recited inclaim 9, wherein the optical pickup head comprises: a digital-to-analogconverting module controlled by the power control module to generate theoperating current; a light-emitting module driven by the operatingcurrent to generate the output power; and a temperature measuring modulemeasuring the first temperature of the light-emitting module to generatethe temperature signal.